Radiobiology(redirected from radiobiologist)
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Related to radiobiologist: radiation biology, radiobiological
the science concerned with the effects of all types of ionizing radiations on living organisms and their communities and on the biosphere as a whole. Radiobiology is related to the scientific disciplines that study the biological effects of the electromagnetic waves in the infrared, visible, and ultraviolet ranges of the spectrum and the radio waves of millimetric and centimetric wavelengths. Radiobiology is characterized by studying high-energy quanta and particles (including alpha particles, electrons, neutrons, positrons, and protons), which have energy greatly exceeding the energy of the ionization of atoms, and which are able to penetrate deeply into an irradiated object and act on all its structures and the molecules and atoms that constitute these structures.
Research on the biological effects of ionizing radiations started almost immediately after their discovery by W. K. Roentgen in 1895 and A. Becquerel in 1896 and the discovery of radium by M. Skłodowska-Curie and P. Curie in 1898. In 1896 the Russian physiologist I. R. Tarkhanov published a study on the possible effects of X rays “on the course of vital functions.” The effects of ionizing radiations on living organisms was studied in the early 20th century in Russia by E. S. London, who published the monograph Radium in Biology and Medicine (1911). In Germany in 1904, C. Peters discovered that cell division is impaired in irradiated cells, and in 1905, P. Linser and E. Helber discovered toxic substances in the blood of irradiated animals. In 1906 the French researchers J. Bergonié and L. Tribondeau observed that cell radiosensitiv-ity is dependent on the intensity and duration of cell divisions (mitoses), as well as on the degree of differentiation. By the 1920’s there were a considerable number of observations on the effects of X-radiation and gamma radiation on a variety of biological specimens. This research, however, was conducted by different specialists—physiologists, zoologists, botanists, and physicians—who were working within their own fields.
In the 1920’s and 1930’s there were many major discoveries and new ideas that hastened the establishment of radiobiology as a science. In 1925 the Soviet scientists G. A. Nadson and G. S. Filippov discovered the mutagenic action of X rays on phycomycetes. In the USA, radiation mutagenesis was studied in the drosophila by H. Muller in 1927 and in higher plants by L. Stadler in 1928. These discoveries laid the foundation for radiation genetics. G. A. Nadson (1920) and P. Ancel and P. Wintemberger (France, 1925) concluded that observed radiation injuries in cells were the result of two conflicting and simultaneous processes—the development of the injury and the process of its restoration. The studies of F. Dessauer in Germany (1922), J. Kroter in Great Britain (1924, 1927), and F. Holveck in France (1928–38) advanced ideas on the discreteness of ionizing radiation and on the absorption of energy as the sum of single interactions of a photon or a particle with individual molecules or cellular structures. In photochemistry, a chemical reaction in a substance can be induced only by the absorbed part of the light that strikes the substance; this general principle can also be applied to ionizing radiation. In the late 1920’s and early 1930’s, J. Crowther, Holveck, and A. La-cassagne analyzed a dose-effect curve on cell death. In order to explain the probability of the curve they introduced the concept of an especially sensitive area in the cell—the target; the ionizing particle strikes the target and produces the observed effect. As a formal generalization of many observed phenomena, the target theory was formulated by the British scientist D. Lea (1946), by N. V. Timofeev-Resovskii, and by the German scientist K. Zimmer (1947).
In the 1940’s and early 1950’s interest in the biological effects of ionizing radiation quickly grew as a result of the rapid development of nuclear physics and technology and the radioactive contamination of the environment by nuclear testing. It was during these years that radiobiology became an independent branch of science. It was confronted with new tasks, including the comprehensive study of radiation injuries to multicellular organisms after their total irradiation, the study of the causes of radiosensitivity differences between organisms, the role of radiation in the origin of harmful mutations, and the study of the patterns and causes for the development of the remote effects of irradiation, which include, for example, a shorter life span, the development of tumors, and a decrease in immunity. Radio-biology also had to deal with such urgent practical matters as the development of various means of radiation shielding and methods for the postradiation regeneration of injuries, the prediction of the hazards to mankind caused by increasing levels of environmental radiation, and the search for new ways to use ionizing radiation in medicine, agriculture, microbiology, and the food-processing industry.
In radiobiology, the 1950’s and 1960’s were characterized by the development of biophysical and biochemical research methods. It became clear that cellular structures and macro-molecules are injured not only by direct contact with quanta and particles but also by water radicals and other substances with low molecular weights and by peroxides, hydroperoxides, semiquinones, and quinones, and other substances that form in cells during irradiation in the presence of oxygen (the indirect effect of radiation).
The major significance of radiation injury to the cell nucleus was demonstrated by R. Zirkle and P. Henshaw in the USA and B. L. Astaurov in the USSR. This research was followed by numerous studies on irradiation-induced disturbances in the structure and metabolism of deoxyribonucleic acid (DNA); direct or indirect injury to DNA is responsible for the genetic effects of radiation. Radioprotectors were discovered during this period; these substances protect animals against radiation. Theoretical prerequisites for effective methods of treating radiation sickness were elaborated during the same period.
Intensive nuclear testing and the general contamination of the earth by radionuclides, especially by the nuclides 90Sr and 137Cs, which have long half-lives, confronted radiobiology with the new task of studying the effects of radiators on the body; these radiators penetrate and become incorporated into it. They are distributed in specific tissues, have different half-lives, and are characterized by the chronic irradiation of cells. The chronic effect of even small doses of radiation became an urgent problem because of the increasingly rapid development of nuclear power.
The construction of nuclear particle accelerators, the use of dense ionizing radiation in medicine, and the exploration of space confronted radiobiology with new problems, including the study of the relative biological effectiveness of pions, high-energy neutrons and protons, and highly charged ions, the simultaneous action of radiation and other factors of spaceflight, including weightlessness and vibration, and the effect of radiation on man’s higher nervous activity in space. At this time, a swiftly growing branch of radiobiology is space radiobiology, which deals with the above problems both in spaceflight and in ground experiments such as those using modern accelerators and special testing units.
The ease of handling microorganisms in radiobiological research has helped accelerate and shape the development of another independent branch of radiobiology—radiation microbiology. The studies of G. A. Nadson laid the foundation for radiation microbiology in the 1920’s. Microorganisms are widely used to determine the general pattern of the effects of ionizing radiation on cells and various intracellular structures, such as organoids. They are also used to determine the mechanisms of radiation mutagenesis and many other problems in radiobiology. Research on the radiosensitivity of microorganisms, some of which show striking resistance to irradiation, has considerably modified ideas on the possible limits for the existence of life under extreme conditions of radiation.
The late 1950’s and early 1960’s were marked by the discovery of the restoration, or repair, of irradiated cells by specific enzyme systems that quickly correct radiation injuries to DNA molecules. This discovery prompted a reexamination of earlier conclusions concerning the development of radiation effects and the danger of injury following chronic exposure to irradiation at small doses. It also led to a review of the causes for the resistance of the cell genetic apparatus. Considerably broadened were ideas about the causes for differences in radiosensitivity between cells, the significance of chromosome size for radiosensitivity, the number of sulfhydryl groups, and the activity of repair enzymes. Formal generalizations on the new facts and ideas were reflected in the stochastic (probabilistic) concept of the biological effects of radiation. Studies on biochemical shifts in irradiated cells and tissues and radiation injuries to the nucleus, mitochondria, biological membranes, and other cell organelles helped to substantiate the structural-metabolic hypothesis of radiation effects. According to this hypothesis, the random nature of radiation effects results from the interaction of the processes that develop in the irradiated organism in molecular and supramolecular structures and in the metabolism of regulatory systems.
The multifaceted tasks facing modern radiobiology have led to the development of radioecology and radiation genetics. Research in the field of radiobiology is the basis for the practical use of ionizing radiation in the radiotherapy of malignant neoplasms and in the development of effective methods for treating radiation sickness. This research has provided the theoretical basis for the use of ionizing radiation to control agricultural pests, to breed new crop varieties (radiation selection), to increase yields by the irradiation of seeds before they are sown, to prolong the storage life of agricultural raw material, and to sterilize medicinal preparations. The data obtained by space radio-biology are essential in ensuring the safety of manned spaceflights. Many discoveries in radiobiology (for example, the discovery of radiation mutagenesis and enzyme repair of radiation injuries to DNA) have substantially widened our knowledge of the general laws of life.
In the USSR, research in radiobiology is conducted in the Institute of Biophysics (in Pushchino), the Leningrad Institute of Nuclear Physics (in Gatchina), and other institutes of the Academy of Sciences of the USSR. Research is also conducted in the institutes of the Ministry of Health of the USSR and the Ministry of Agriculture of the USSR and in many subdepartments of higher educational institutions.
The principal research centers outside the USSR include the Brookhaven National Laboratory and the Biology Division of the Oak Ridge National Laboratory (USA), the Radium Institute and the Biology Division of the Atomic Center in Saclay (France), the Radiobiology Laboratory of the Atomic Energy Research Establishment in Harwell (Great Britain), the Institute of Biophysics of the Academy of Sciences of Czechoslovakia in Brno, the Institute of Biophysics in Frankfurt am Main, the Nuclear Research Center in Karlsruhe and the Institute of Radiation Botany in Hamburg (Federal Republic of Germany), the Radiobiology Section of the Bhabha Atomic Research Center in Trombay (India), and the National Institute of Radiological Sciences in Chiba (Japan).
In 1955 the General Assembly of the United Nations appointed a special Scientific Committee on the Effects of Atomic Radiation; 20 countries participated in collecting information on the radiation situation on earth and on the possible biological consequences of irradiation on man. This information was reported regularly to the UN between 1958 and 1972.
The principal periodicals on radiobiology include Radio-biologiia (since 1961), Radiation Research (New York, since 1954), International Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine (London, since 1959), and Radiation Botany (London-New York, since 1961). The International Association for Radiation Research, the European Society for Radiation Biology, and the Scientific Council for Problems in Radiobiology of the Academy of Sciences of the USSR regularly sponsor national and international symposiums (the first was held in Denmark in 1953), conferences, and congresses (the first was held in the USA in 1958).
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A. M. KUZIN